In connection with harvesting, a lot of logging waste which is suitable for use as a fuel is developed in the forest, wherein the logging waste is normally crushed to chips and combusted in furnaces. The logging waste consists of branches which come off in connection with the delimbing of tree stems, when the tree stem is manipulated, for example, at the harvester head of a forest working machine. The same device is also used to cut the top of the tree stem which is left as logging waste. The logging waste may also consist of other small and thin trees or brushwood.
The logging waste can be compressed by means of various devices to a compact bundle with a circular cross-section and a varying length, wherein it is referred to as a so-called stock of brushwood, which thus consists of compressed and bound branches and tops. One such device is presented in Swedish patent publication 511379, wherein the device consists of a compressing element of two parts. Material is fed into the first compressing chamber and compressed into the next compressing chamber. In the second compressing chamber, the material is compressed further, and simultaneously a cord or a wire is wound around it so that it would remain in the compressed state. The latter compressing chamber grips the formed bundle and pulls it forward, after which the compressing chamber returns to its initial position to continue the compressing and the binding. The bundle is cut to a desired length by a cutting apparatus. The bundling device is mounted on the frame of a forest working machine where also a boom assembly and a loader are placed for manipulating the logging waste and the bundles.
Another known device is presented in the Swedish publication 458355 and in the corresponding Finnish publication 59904.
In the known devices, several revolutions of a cord are wound around the bundle, but the cord is left unlocked, when the binding device moves to a new binding point. The cord is cut in connection with sawing of the bundle, but the end of the cord is not fixed. In one bundle, there are about 5 binding points and 2 to 4 revolutions of the cord. For binding the ends of the bundle, several revolutions of the cord are used.
It has also been found in practice that the cords are loosened during the handling of the bundles and also at the stage when the bound bundle is no longer subjected to compression by the chambers. Because of the high compressibility of logging waste, the material must be compressed by an auxiliary chamber or auxiliary means to achieve successful binding. When the compression ceases, the material tends to return and exerts a force effect on the cords. As a result of the loosening of the cords, the bundle may open up and the necessary volume may increase, which is not economical in view of transportation and energy consumption. The bundles are difficult to process further if they are not held together by the cords. The cords may also be broken as a result of, for example, rotting or a strong force effect. Impregnated cords are expensive to use and may be hazardous waste. The quantity of cord used in one bundle is about 30 to 40 m.